1. Field of the Invention
This invention relates to a scroll compressor for compressing refrigerant or air in, for example, referigerators, air conditioners, and so forth.
2. Discussion of Background
This type of scroll compressor is disclosed in Japanese Patent Application No. 64571/1984, which is in such a construction as shown in FIG. 9 of the accompanying drawing.
Explaining this scroll compressor in reference to the drawing, it is constructed with a casing 1 for the scroll compressor, which comprises an upper shell 2 and a lower shell 3; a main shaft 4 provided in the interior of the casing 1 and having therein an oil-feeding passage 5 and an eccentric hole 6; an orbiting scroll member 7 which is supported in the eccentric hole 6 of the main shaft 4 through an orbiting bearing member 8, and is provided with a scroll end plate 7a and a spiral wrap 7b; and a stationary scroll member 9 to be assembled with the orbiting scroll member 7, and having a scroll end plate 9a and a scroll wrap 9b. In the scroll end plate 9a of this stationary scroll 9, there is formed an outlet pocket 10 opening in the axial direction. An orbiting shaft 11 is integrally fitted in the above-mentioned eccentric hole 6 formed in the scroll end plate 7a of the above-mentioned orbiting scroll 7. Between both orbiting scroll 7 and stationary scroll 9, there are formed an inlet chamber 12 having an inlet port 12a for sucking fluid in the above-mentioned casing 1 and a compression chamber 13 having the innemost (or central) pocket 13a communicatively connected with the above-mentioned outlet pocket 10. Reference numerals 14 and 15 designate respectively an upper bearing support and a lower bearing support; a numeral 18 refers to a thrust bearing which is installed on the upper bearing support 14 out of the two bearing supports 14, 15 to hold thereon the above-mentioned orbiting scroll member 7; a numeral 19 refers to an Oldham coupling which is disposed around this thrust bearing 18 to prevent the orbiting scroll member 7 from its rotation and cause it to perform revolution, i.e., orbiting movement; a reference numeral 20 denotes a motor rotor which is housed in the interior of the above-mentioned casing 1 and fixed on and around the above-mentioned main shaft 4; a reference numeral 21 represents a motor stator which is provided around the motor rotor 20 and fixed on the above-mentioned lower bearing support 15; a reference numeral 22 designates a shielding plate which is disposed below the motor stator 21 and has a hole 22a formed therein to permit passage of the main shaft 4 therethrough; a numeral 23 refers to lubricating oil stored below this shielding plate 22; a reference numeral 24 designates a cylindrical cap member for an oil pump, which is fitted at the extreme end of the main shaft 4 and immersed in the lubricating oil 23; a numeral 25 refers to a glass terminal which is fixed on the upper shell 2 and to which a lead wire (not shown in the drawing) from the motor stator 21 is connected; a numeral 26 is a balancer chamber defined in the lower bearing support; a numeral 27 refers to a first balancer accommodated in this balancer chamber 26 and fixed on the main shaft 4; a numeral 28 refers to a second balancer which is provided below the first balancer 27 and fixed on the motor rotor 20; reference numerals 29 and 30 are respectively oil returning passageways formed in the upper bearing support 14 and the lower bearing support 15, and opening in the axial direction; 31 denotes legs for holding firmly the overall compressor; 32 designates an oil sump, and 33, 34 denote respectively an inlet tube and an outlet tube.
In the scroll type compressor of the above-described construction, when the main shaft 4 starts to rotate by electric conduction through the motor stator 21, the rotational force of this main shaft is transmitted to the orbiting scroll member 7 through the orbiting bearing 8, whereby this orbiting scroll member 7 moves, while maintaining a certain definite angular posture with respect to the upper bearing support 14. During this movement of the orbiting scroll member 7, compression of fluid is effected in the compression chamber 13, whereby the fluid is introduced into the casing 1 from the inlet tube 33, as shown by an arrow in dash, to cool the upper part of the motor stator 21, after which it passes through the outer peripheral passage (not shown in the drawing) of the upper bearing support 14, and is discharged outside the casing 1 from the outlet tube 34 by way of the inlet port 12a, the inlet chamber 12, the compression chamber 13 and the outlet pocket 10. At this instant, the lubricating oil 23 in the casing 1 is sucked in through the cylindrical cap member 24 due to the centrifugal force caused by rotation of the main shaft 4, is elevated in and through the oil feeding passage 5, and is fed to the orbiting bearing 8 and the main bearing 16. Thereafter, this lubricating oil 23 passes through an oil feeding groove (not shown in FIG. 9) of the thrust bearing 18 and discharged outside in the radial direction from the center of the thrust bearing 18, and is returned to the oil sump 32 situated below the shielding plate 22 through the oil returning passage 29, the balancer chamber 26, the oil returning passage 30, and the hole 22a. In this case, since a gap between the scroll end plate 7a and the Oldham coupling 19 is set in a minute size, any outflow of the lubricating oil 23 through this gap into the inlet chamber 12 can be prevented.
By the way, there are two ways of forming the oil feeding passages (or grooves) 41 in the thrust bearing 18: the one is a radial type as shown in FIGS. 10 and 11, wherein the oil feeding passages are formed radially to extend from the inner peripheral edge 18a to the outer peripheral edge 18b; and the other is an involute type as shown in FIGS. 12 and 13, wherein the oil feeding passages are formed as such. The thrust bearing 18 as a whole is constructed with a bearing layer 18c made of aluminum alloy, PTFE (polytetrafluoroethylene resin) and others, and a metal lining layer 18d made of rolled steel plate to support the bearing layer 18c. It is a usual practice to form the oil feeding passages 41 by press-forming, in case the thrust bearing 18 is made of aluminum alloy, and the depth D of the passage ranges from 0.3 to 0.6 mm. When the thrust bearing 18 is made of aluminum alloy and the depth D of the oil feeding passage is deeper than 0.6 mm, or when the thrust bearing is made of PTFE, it is a usual practice to form the passages by cutting work.
On the contrary, when the depth D of the oil feeding passage 41 is smaller than 0.6 mm (that is, when the grooves 41 are to be formed by the press-forming), it has been done generally to enlarge the breadth W of the oil feeding passage, or shorten the length L of the passage, or reduce the number N thereof, taking into consideration easy flow of the lubricating oil 23 in and through the oil feeding passages 41. On account of such designing of the oil feeding grooves, there has been a problem such that the effective area of the bearing part 18e of the thrust bearing 18 becomes smaller, which in turn increases the load to be imposed on the unit area of the bearing part to thereby cause abnormal wear and burning of the bearing part 18e.
In the case of forming the oil feeding passage 41 by the cutting work, the depth D of the groove can be arbitrarily determined, which, however, brings about inconveniences such that the arbitarary setting of the depth not only makes the machining work complicated, but also it causes deformation in the thrust bearing 18 due to the machining work.
Further, in the conventional scroll type compressor, the gap between the scroll end plate 7a and the Oldham coupling 19 should be set in a minute size with a view to inhibiting flow of the lubricating oil 23 out into the inlet chamber 12 as shown in FIG. 14 of the accompanying drawing, on account of which the plate thickness of the thrust bearing 18 and the Oldham coupling 19 needs to be established in a precise dimension. In addition, the flatness of a thrust bearing fitting surface 14a and an Oldham coupling sliding surface 14b of the upper bearing support 14 as well as a sliding surface of the Oldham coupling 19 (not shown in the drawing) should be rendered with high precision, which makes the machining work complicated and results in high production cost. For example, if the minute clearance g is set in a size of 70 .mu.m or so, the oil circulating quantity (i.e., a ratio of a weight of the lubricating oil discharged outside the casing 1 from the outlet tube 34 to a weight of refrigerant during circulation of the refrigerant during the operation of the scroll type compressor) can be set below 1% as a permissible circulating quantity.
The conventional scroll type compressor, therefore, has adopted a design as shown in FIGS. 15, 16 and 17 of the accompanying drawing, wherein oil feeding passages 51, each having a terminal part 51a, are formed in the thrust bearing 18, and a part of this oil feeding passage 51 is communicatively connected to the oil returning passage 29 of the upper bearing support 14 so as to fill a space between the scroll end plate 7a and the thrust bearing 18 with the lubricating oil 23 as shown in FIG. 18, thereby establishing the oil circulating quantity to be 1% or below.
In this type of scroll compressor, however, since the construction in such that the oil feeding passage 51 is closed by its terminal part 51a, the quantity of the lubricating oil 23 to flow out in the radial direction of the thurust bearing 18 becomes extremely small with the consequence that the oil feeding quantity to the Oldham coupling sliding groove of the orbiting scroll member 7 and to the Oldham coupling sliding part of the upper bearing support 14 reduces considerably, which tends to cause rapid wear of the Oldham coupling 19.